The phrase "unhealthy social life" has taken on a new meaning, according to a recent study published in the journal Health Psychology

. First-year Carnegie-Mellon University students who felt lonelier and were more socially isolated than their peers mounted a weaker immune response to a flu shot than did other students, report researcher graduate student Sarah Pressman and psychologist Sheldon Cohen, Ph.D., who led the study. Of the 37 male and 46 female freshmen participants, those whose social networks consisted of fewer people they either knew well or were in regular contact with exhibited a poorer response to one strain of the vaccine, A/Caledonia, than those with greater social ties. And students who said they felt lonely had a poorer immune response to the same strain up to four months after getting the shot. The researchers speculate that the stress of loneliness may translate into weakened immunity, so if you're planning to get a flu shot, take some friends with you.